In US2003/0008407 a non-invasive diagnostic system is described for monitoring the condition of an entity, e.g. the diabetic condition of a human being or animal. In this system a number of volatile or gaseous compounds secreted by the entity or body that characterize the condition or state are determined. The obtained data are processed in such a way that conclusions may be drawn concerning the condition or state.
An important application is to monitor human beings with diabetes mellitus, diabetes for short, a chronic disorder of the glucose metabolism in the body. Because the pancreas, that produces the hormone insulin that controls the uptake of glucose in cells, does not work or works insufficiently, blood glucose is not absorbed adequately or at all. People suffering from diabetes have an increased risk of cardiovascular diseases, high blood pressure, neurological disorders, skin disorders, deterioration of the retina, kidney disorders and impotence to name but a few, which can lead to serious debilitation and in extreme cases to an early death. The number of diabetics worldwide is estimated at 100-150 million and the number of people diagnosed with diabetes has increased rapidly over the past decades from 2-3% to 5-6%.
As yet there is no cure for diabetes, but the above complications can be prevented or at least reduced or postponed to a considerable extent by an adequate control of the blood glucose level. This can be done by medicinal treatment or administration of insulin in combination with a suitable diet and lifestyle. A good—in ideal cases a continuous—control of blood glucose levels is of prime importance. Ideally values of between 4 and 10 mmole/1 (the extreme values of a non-diabetic person) should be maintained.
In US2003/0008407 only a limited number of known possible sensors and detection facilities are cited briefly—an oscillator, a sensor based on electrical conductivity and traditional HPLC, GC or MS methods.
US 2005/0010090 provides a more extensive overview of known methods and techniques to determine blood glucose levels. Here a distinction is made between methods referred to as ‘traditional invasive’, ‘alternative invasive’, ‘non-invasive’ and ‘implantable’ and techniques such as ‘direct’ and ‘indirect’ glucose measurement. In a traditional invasive method a sample of arterial or venous blood is drawn by means of a needle, or a capillary blood sample is taken by means of a lancet. However, this method is considered to be inconvenient and piercing the skin is painful. Also the analysis of the sample thus obtained yields only a random indication. As has been said before, an adequate control of blood glucose levels requires a continuous or at least frequent (during night and day) measurement. It will be obvious that this entails unacceptable stress for the patient and is practically impossible to implement.
In an alternative invasive method the alternative can refer to the site where the sample is taken but often it refers to an alternative way to draw a sample of interstitial fluid, blood or a mixture of both. This can be done by (i) piercing the skin with a laser, (ii) to enhance the permeation of interstitial fluid through the skin electrically, or (iii) to locally apply a reduced pressure to the skin in order to stimulate the permeation of interstitial fluid through the skin. To determine the glucose levels in the obtained biological samples spectrophotometrical methods (Raman, fluorescence, visible light, UV and IR) are used besides electrochemical, (electro)enzymatic or colorimetrical methods. The glucose levels can be determined directly or indirectly via a number of compounds that characterise the glucose level or diabetic condition. In practice, such known methods and techniques turn out to be relatively laborious and difficult to perform by a layman, insufficiently fast or accurate, often are insufficiently reliable, often costly and unsuitable for (semi)-continuously or automatically measuring the blood glucose levels. To date, the cited shortcomings prevent a (widespread) application of these techniques. In a non-invasive method no sample is taken but a physiological parameter is determined by studying an area of the body and through a certain algorithm the glucose level in the blood is deduced. In many cases a form of spectroscopy is used, but thermal or electrical methods are used as well. Such known techniques again prove to be fairly laborious, difficult to perform by a layman, and expensive. Consequently non-invasive methods based on the mentioned techniques are not applied (on a wider scale).
Furthermore a number of types of short-term or long term implantable glucose sensors are under development. U.S. Pat. No. 5,377,008 and U.S. Pat. No. 6,429,023 describe optical devices for determining characteristics of liquids, based on a sensor surface linked to a (Mach-Zehnder) interferometer. U.S. Pat. No. 6,618,536 describes a similar device with which in principle all kinds of parameters such as air humidity, chemical composition of gases or liquids and variations in optical refraction index and temperature can be measured. Such devices prove to be very sensitive with very low detection limits. Moreover, they can be made to be selective for one or more specific compounds.
It can be concluded that there is very big need for an affordable, user-friendly system with which the state of health, in particular the diabetic condition of a human can be determined continuously, or at least a sufficient number of times a day, pain-free or at least with minimal stress, sufficiently precise and preferably automatically. In practice none of the known systems, methods and techniques fulfils this need. The purpose of the invention is to provide such a system.